1. Field of the Invention
This invention relates generally to magnetic recording heads, particularly to perpendicular recording heads that produce their recording magnetic fields perpendicularly to the recording medium. More specifically it relates to a shield formed about the recording pole in such a configuration that stray magnetic fields are not permitted to cause erasures of nearby recorded tracks.
2. Description of the Related Art
The increasing need for high recording area densities (up to 500 Gb/in2) is making the perpendicular magnetic recording head (PMR head) a replacement of choice for the longitudinal magnetic recording head (LMR head).
By means of fringing magnetic fields that extend between two emerging pole pieces, longitudinal recording heads form small magnetic domains within the surface plane of the magnetic medium (hard disk). As recorded area densities increase, these domains must correspondingly decrease in size, eventually permitting destabilizing thermal effects to become stronger than the magnetic interactions that tend to stabilize the domain formations. This occurrence is the so-called superparamagnetic limit. Recording media that accept perpendicular magnetic recording, allow domain structures to be formed within a magnetic layer, perpendicular to the disk surface, while a soft magnetic underlayer (SUL) formed beneath the magnetic layer acts as a stabilizing influence on these perpendicular domain structures. Thus, a magnetic recording head that produces a field capable of forming domains perpendicular to a disk surface, when used in conjunction with such perpendicular recording media, is able to produce a stable recording with a much higher area density than is possible using standard longitudinal recording.
A significant problem with magnetic pole structures that are currently used to produce perpendicular fields, is that the fields tend to exhibit significant lateral fringing, thereby producing unwanted side-writing (writing in tracks adjacent to the intended track). This problem is much more evident in the perpendicular writing head than in the longitudinal writing head, even when the perpendicular head is shielded laterally (on its sides) to contain the fringing fields.
Even when PMR writers added side shields to the more usual trailing edge shields, it was found that the side shields contained sufficient amounts of magnetic flux to cause erasures along adjacent tracks. Referring to prior art FIG. 1, there is shown a perspective illustration of a magnetic pole of a PMR writer (10) surrounded on three sides by a magnetic shield (20). The air bearing surface of the main magnetic pole tip (15), shown here with a truncated triangular shape, emerges from a substantially rectangular opening (25) in the shield (20). This opening has a trailing edge (22) that is between the two corners (30), and two lateral edges (24), which define the inner edges of the side shields.
It is found that enough magnetic flux emerged from the edges (24) of the side shields to cause significant erasures on portions of the recording media laterally disposed to the position of the main magnetic pole. Depending on the distance between the pole tip and the edges (24) and corners (30) and the skew angle of the application (angle between the center line of the pole-tip ABS and the direction of motion along the recording track), the erasures actually went beyond adjacent tracks, causing what we refer to as skip track erasures.
If the shield corners (30) are reasonably close to the main pole, the erasure produced by the shield flux can be merged with the usual adjacent track erasures caused by the diverging flux of the pole tip itself. In either case, the reduction of the side erasures caused by the shield flux is necessary to create improved area density of recorded tracks (TPI, “tracks per inch”).
Among the efforts in the prior art to address the adverse effects of field fringing is the side shielded head of Sin (US Patent Application Publication US2009/0002885) and the side shielded head of Mao et al. (U.S. Pat. No. 7,035,062). Neither of which provide the improved fringing control of the present invention.